release/1.6.0: update site configs and documentation for Hercules/Nautilus/Narwhal-Intel/S4/Discover

[climbfuji]

Summary

Update site configs and documentation for spack-stack-1.6.0 for:

• Hercules
• Nautilus
• Narwhal (Intel only so far)
• S4
• Discover

Also: submodule pointer update for spack for a PR required to build on these platforms (spack PR JCSDA/spack#386 already merged).

Please note the workaround for Narwhal that uses an external node.js that is supplied via the compiler config while the correct solution (for after release 1.6.0) is being worked on (see #928 and spack/spack#41899).

Testing

Describe the testing done for this PR.

Applications affected

n/a

Systems affected

See above list

Dependencies

• release/1.6.0: bug fix for in py-gevent to build with Intel / oneAPI compilers spack#386 (already merged)

Issue(s) addressed

Working towards #924
Resolves #921

Checklist

• This PR addresses one issue/problem/enhancement, or has a very good reason for not doing so.
• These changes have been tested on the affected systems and applications.
• All dependency PRs/issues have been resolved and this PR can be merged.